1. Field of the Invention
The present invention relates to a radio communication apparatus and a method of transmitting a retransmission packet with multiple resource blocks.
2. Description of the Related Art
Hybrid ARQ (Hybrid Automatic Repeat request) includes existing ARQ functions (error detection function and retransmission function) and an error correction function. According to Hybrid ARQ, the number of packet retransmissions can be reduced by transmitting an error correction code in advance.
There are two types of Hybrid ARQ schemes as shown in FIG. 1. One scheme is referred to as Synchronous ARQ and the other scheme is referred to as Asynchronous ARQ.
According to Synchronous ARQ, packets are retransmitted at predetermined retransmission timings. For example, a transmission packet at a timing #0 (S00) is detected as an error packet, corresponding retransmission packets can be transmitted at timings #0 (S10 and S20). In other words, retransmissions are performed at frames which are integral multiples of RTT (Round Trip Time) or control loop delay.
Synchronous ARQ has an advantage that the process number indicating the original transmission packet for retransmission packets does not have to be provided as control bits and thus overhead can be reduced, because retransmission timings are determined in advance. Synchronous ARQ also has an advantage that retransmission processing can be simplified. However, Synchronous ARQ has a disadvantage that it does not have flexibility in scheduling retransmission packets and allocating TTIs (Transmission Time Intervals or subframes) to them, because of the constraints of retransmission timings. Furthermore, when a packet cannot be retransmitted after one RTT from the initial transmission packet, the packet has to wait for at least two RTTs and thus delay may be increased.
On the other hand, according to Asynchronous ARQ, packets are retransmitted at any timing after one RTT. For example, a transmission packet at a timing #0 (A00) is detected as an error packet, corresponding retransmission packets can be transmitted at any timing (TTI) after A10. In other words, retransmissions are performed at any timing (A10-A25) after one RTT from the transmission packet. It is noted that Asynchronous ARQ is used in HSDPA (High Speed Downlink Packet Access) (for example, Non-Patent Reference 1).
Asynchronous ARQ has an advantage that it has flexibility in scheduling retransmission packets. In addition, when a packet cannot be retransmitted after one RTT from the initial transmission packet, the packet can be transmitted after timings of (RTT+1) rather than after two RTTs and thus delay may be reduced. However, Asynchronous ARQ has a disadvantage that retransmission processing can be complicated. Furthermore, the process number has to be provided as control bits and thus overhead can be increased.
[Non-Patent Reference 1] 3GPP TS 25.212, “Multiplexing and channel coding (FDD)”